Prosthesis template for use in a robot-aided system for surgery

ABSTRACT

A prosthesis template for aiding in the determination of a desired position of a prosthesis relative to a bone, the prosthesis having an exterior surface that simulates the exterior surface of the bone and an interior surface comprised of one or more contact surfaces to which the prepared bone must conform to provide an adequate fit of the prosthesis. The template comprises a template member having an interior surface which corresponds to an exterior surface of the prosthesis, whereby the template can be positioned adjacent to the bone and thereby provide means for evaluating a desired position of the prosthesis exterior surface.

This is a divisional of prior application Ser. No. 08/072,466, filed onJun. 4, 1993, now U.S. Pat. No. 5,403,319, which in turn is a divisionalof application Ser. No. 07,934,713, filed on Aug. 24, 1992, now U.S.Pat. No. 5,236,432, which in turn is a divisional of application Ser.No. 07/606,521, filed on Oct. 31, 1990, now U.S. Pat. No. 5,154,717,which in turn is a divisional of application Ser. No. 07/186,345 filedon Apr. 26, 1988, now U.S. Pat. No. 4,979,949, the benefit of the filingdates of which are hereby claimed under 35 U.S.C. §120.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods applicable insurgical situations in which the precise positioning of a tool inrelation to a patient is an integral part of the surgery. Moreparticularly, the present invention utilizes a programmable robot in asystem for determining a reference position for certain surgical tasks,precisely determining the position for a specific tool relative to thereference position, positioning the tool, and rigidly holding the toolto aid the surgeon in a more efficient and accurate completion of thetask.

BACKGROUND OF THE INVENTION

During orthopedic surgery, it is often the case that surgeons arerequired to make surgical alterations to bone. Such alterations includebut are not limited to making cuts in bone, drilling holes in bone, andaffixing a plate, screw, nail, or prosthesis to bone.

When making such alterations, it is desirable that the alteration berealized in a manner which precisely conforms to the operative plan ofthe surgeon. Among the aspects of a surgical alteration which requirecareful control are: (1) the alignment of the cut, hole, plate, screw,nail, or prosthesis with respect to the anatomy of the patient; (2) ifthere is more than one bone cut and/or hole, the relative alignment ofthe cuts and holes with respect to each other; and (3) if a plate,screw, nail, or prosthesis is to be fixed to bone, the alignment of thecuts and/or holes with respect to the plate, screw, nail or prosthesis.

Current surgical techniques utilize limited mechanical means to assistthe surgeon in making bone alterations. However, existing techniques donot suffice to ensure that perfect or nearly perfect alterations can beachieved routinely. Where practical, it is desirable to enhance thesurgeon's decision-making process by providing accurate solutions topurely geometric problems posed by surgery, while leaving finalpositioning decisions up to the surgeon. When the surgeon is providedwith accurate geometric solutions, the quality of the overall subjectiveevaluation should be improved.

An example of a surgical procedure that requires accurate geometricsolutions, as well as the evaluation of specific patient physiologicalcharacteristics, is total knee arthroplasty (TKA), which is a total kneereconstruction surgery. The anatomic knee is a remarkable mechanism.Contrary to first impression, it is not a simple hinge. Rather, thefemur and tibia move relative to each other with a complex mixture ofrolling and sliding motions. The stability of the joint comes entirelyfrom soft tissue structures, not from bone geometry. The majorstabilizing ligaments are the medial and lateral collateral ligaments,and the anterior and posterior cruciate ligaments.

In total knee arthroplasty, the distal femur and the proximal tibia areresected and are replaced by prosthetic components made of metal andplastic. The most successful designs are unconstrained prostheses thatclosely mimic the natural anatomy of the knee. Like the anatomic knee,unconstrained designs allow the femur and tibia to roll and sliderelative to each other. They depend on the natural ligamentousstructures of the knee to stabilize the reconstructed joint. Total kneereconstruction surgery is conceptually simple. The knee is flexed, thepatella moved to one side to give access to the joint, and thedegenerated surfaces of the femur and tibia are cut away. The bone cutsare made to fit femoral and tibial prosthetic components, which areavailable in a wide variety of sizes and styles. These are generallycemented into place, using polymethyl methacrylate (PMMA). One newtechnique uses no cement. Rather, bone grows into a porous backing onthe prosthetic component. This is termed porous-ingrowth fixation.

Each year, approximately 100,000 people undergo a TKA. TKAs are oftenperformed in people whose knees have become so painful, because ofprogressive arthritic changes, that they are unable to rise from achair, walk, or climb stairs. For these people, total knee arthroplastycan provide a return to near-normal, pain-free life.

A great deal of developmental technology has gone into perfecting thefemur prostheses used in TKAs. However, the technology for positioningthe prosthesis properly on the femur has not similarly advanced.Ideally, the bone cuts should be (1) an exact press-fit to thecomponents, and (2) in proper alignment with respect to bones and softtissues. Failure to achieve these goals will result in poor kneemechanics and/or loosening of the components, leading eventually tofailure of the reconstruction.

At present, the surgical instrumentation used in total knee arthroplastyconsists of hand-held saws which are guided by simple cutting blocks andmechanical jig systems. There is abundant evidence in the literaturethat these tools do not suffice to do a good job. First, most prostheticcomponents are not put in with perfect alignment, and misalignment ofthree to five degrees or more is not uncommon. Second, prostheticcomponents do not fit perfectly on the bone, and there are inadvertentgaps between the cut surface of the bone and the prosthesis. Third,there is a learning curve associated with arthroplasty technique. Thefirst fifty knees a surgeon does are not as good as subsequent knees.

The primary goals of the surgeon during total knee arthroplasty are:proper alignment of the reconstructed knee, stability of thereconstructed knee, and press-fit of the components to the bone. Withrespect to alignment, the knee should neither be knock-kneed orbowlegged, to ensure that the medial and lateral sides of the componentsbear equal loads. Asymmetric loading leads to early failure. Inaddition, the ligaments of the knee should provide stability at allangles of flexion, as they do in the anatomic knee. If the ligaments aretoo tight, they will restrict the motion of the knee. If they are tooloose, the knee will "give way" during use.

Finally, if a prosthetic component is even slightly loose, then eachstep will "rock" the component against the bone. The bone soon givesway, and the reconstruction fails. Ideally, the prosthesis is apress-fit to the cut bone at the time of surgery. This minimizesmicro-scale rocking motions. Press-fit is especially important for aporous ingrowth prosthesis, since even a one-millimeter gap betweenprosthesis and bone is too large for the ingrowth process to bridge.

These goals are simple to state, but difficult to achieve in theoperating room. To understand the problems, consideration should begiven to all the ways malalignment can occur. There are three differentways a component can be malaligned in orientation. These correspond torotations of the component away from the desired orientation along theinternal/external, varus/valgus, and flexion/extension axes. Similarly,there are three different ways to malposition a component by translationalong an axis. These correspond to translations along themedial/lateral, proximal/distal, and anterior/posterior axes.

Thus, to achieve good alignment and good ligament balance, surgeons mustmentally manipulate three translational and three orientationalvariables for each of the femoral and tibial components, or twelvespatial variables in all. Margins for error are small. Repositioning theprosthetic component by even one millimeter has an appreciable effect onthe stability of the knee. Moreover, each knee presents its own specialproblems. It is frequently the case that the knee has a preexistingdeformity which must be taken into account.

In addition, the surgeon must also take care that the bone surfaces arepressfit to the component. This involves five cut planes and two drillholes for a typical femoral component, and one cut plane and two drillholes for a typical tibial component, for a total of ten separatecutting operations. In each case, imprecision of one millimeter or lesscan have significant consequences, especially for porous-ingrowthprostheses.

It is a remarkable fact that present-day surgical instruments for totalknee arthroplasty could have been manufactured in the nineteenthcentury. The essential features of present-day instrumentation systemsare their reliance on hand-held oscillating saws to make bone cuts, andmechanical jigs with slots and cutting blocks to help align the cuts.Considerable ingenuity has been applied to optimizing instrumentationsystems of this type, and there are dozens of variations on the market.Nonetheless, poor alignment and inaccurate cuts are common problems whenusing these mechanical instrumentation systems.

Poor alignment occurs when femoral and tibial cutting jigs are notproperly aligned with respect to the hip, the ankle, and the stabilizingsoft tissues of the knee. This can happen because the surgeon is misleadby the anatomic landmarks used by a given system, because the landmarksare concealed by fat and muscle, because preoperative deformities exist,or because the jig has shifted slightly during the procedure. The besttest of alignment is flexion of the newly reconstructed knee.Unfortunately, by the time such a test can be made, the bone cuts havebeen made, and it is too late to change the alignment of the components.

Inaccurate cuts occur when the various cuts and drill holes do notprecisely mate with the surfaces of the prosthetic components, possiblyas the result of errors which accumulate during placement and removal ofthe various cutting blocks. Also, there is inherent inaccuracyassociated with a flexible, oscillating saw blade resting on a cuttingblock or in a slot. The blade tends to "sky" when it encounters a densesection of bone. This tendency is resisted by canting the hand-held sawin a downward direction.

There is ample evidence in the published literature that the presentstate of total knee arthroplasty is not satisfactory. Cameron H. U.,Hunter G. A. in: Failure in Total Knee Arthroplasty, 170 ClinicalOrthopaedics and Related Research: pp. 141, 146, 1982, noted, " t!heresults of total knee arthroplasty range from an acceptable 5.4% failurerate at five years to an abysmal 70% failure rate at three years.Failure rates of this magnitude indicate that many revisions are beingperformed." Bryan R. S., Rand M. J. in: Revision Total KneeArthroplasty, 170 Clinical Orthopaedics and Related Research: pp.116-122, 1982, state that, " p!roper component alignment is of criticalimportance" and that " f!ailure to obtain appropriate componentorientation, axial alignment, and soft tissue balance predisposesimplants to loosening and failure." Hood R. W., Vannie M., and InstallJ. N., as noted in, The Correction of Knee Alignment in 255 ConsecutiveTotal Condylar Knee Replacements, 160 Clinical Orthopaedics and RelatedResearch: pp. 94-105, 1981, found in a series of 225 knees that, "e!leven per cent of the knees in this series were outside the alignmentlimits selected. This may reflect extremes of body habitus but, moreimportantly, indicates that deficiencies in instrumentation stillremain." Hvid I., Nielsen S. in: Total Condylar Knee Arthroplasty, 55Acta Orthop Stand 55: pp. 160-165, 1984, found in a study of 138 kneesthat although "the aim was to place the tibial component at right anglesto the tibial axis," only "53 per cent were within four degrees of tiltin any direction." Some of their components were eight degrees or moreout of alignment. In summary, there is ample evidence that with existinginstrumentation surgeons cannot obtain good alignment routinely in totalknee arthroplasty.

As is evident from the less-than-satisfactory clinical results, thetheory and practice of jig-assisted knee surgery are two differentthings. In practice, total knee arthroplasty is largely aseat-of-the-pants procedure. Surgeons recruit every pair of eyes in theoperating room to judge how a contemplated cut "looks" from a variety ofangles. Equally important is a steady and practiced hand on the cuttingsaw, and a sound understanding of the biomechanics of the knee joint.

The conventional TKA requires that the surgeon attempt to achieve exactphysiologically correct relationships and to make geometrically exactcuts with inexact methods. As discussed above, both the position andquality of the cuts and bores greatly affect the success of theoperation. While the background of a TKA has been described, numeroustypes of surgeries present the same problem of integrating geometricanalysis with a subjective evaluation of physiological factors. Examplesof such surgeries are osteotomies and ligament repairs. In the majorityof these operations, certain mechanical devices, such as the jig systemsdescribed above, have been developed to aid in the operation. Theexactness of these mechanical devices varies and, thus, so do theefficiencies resulting from their use. However, most surgical proceduresthat are not solely based on subjective medical decisions will sufferfrom some inaccuracies based on the fact that surgeons have a limitedcapacity for making independent exact geometric calculations andcarrying out tasks based on those calculations.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a system and methodfor facilitating the performance of a surgical bone alteration task byaccurately positioning a tool relative to the patient's bone. Theillustrative example of a total knee arthroplasty (TKA) of a femur isused.

In one preferred embodiment, a system according to the present inventioncomprises bone immobilization means and a robot. The bone immobilizationmeans supports the patient's bone in a fixed position with respect to areference structure. The robot comprises a base, a mounting member and amanipulator. The base is fixed in position with respect to the referencestructure. The manipulator connects the mounting member to the base soas to permit relative movement between the mounting member and the base.The robot also includes attachment means for securing a tool to themounting member. Finally, the system includes means for causing themounting member to move relative to the reference structure in responseto movement commands, so that the tool can be moved to a position tofacilitate performance of the task. The movement commands are preferablyprovided by task control means that includes memory means for storingdata and control programs, and control processing means for processingthe control programs to generate the movement commands.

Preferably the system also includes a template attachable to themounting member. The template may be positioned such that apredetermined feature of the template is in a desired position relativeto the bone. For a TKA procedure, the template feature may represent asurface of a prothesis to be mounted on the patient's bone. With thetemplate in the desired position, the reference position of the templateis recorded in a "world" coordinate system that is fixed with respect tothe reference structure. The reference position may therefore becombined with a geometric database that includes data representing thegeometric relationships relevant to the performance of the task, togenerate movement commands that cause the robot to move surgical toolsinto desired tool positions during subsequent stages of the operation.Preferably, the reference position is determined by placing the robot ina passive mode in which the mounting member may be moved manually by anoperator. The operator can then mount the template to the mountingmember, move the template and mounting member such that the template isproperly positioned with respect to the bone, and then cause the systemto record the reference position. The robot can then be returned to anactive mode in which the mounting member moves in response to movementcommands.

In another preferred embodiment, the present invention provides a boneimmobilization device to be used in a surgical procedure requiring therigid positioning of a bone throughout the procedure. The boneimmobilization device rigidly secures a bone in relationship to areference structure such as an operating table. The bone is insertedthrough a frame and rigidly suspended relative to the frame by fixationmeans attached to the frame and the exposed bone. The frame is securedrelative to the reference structure by an adjustable support means. Theframe can be disassembled into an upper section and a lower section forease of positioning the bone as well as for removal of the bone in caseof an emergency.

In accordance with further aspects of this invention, the fixation meansinclude two coacting gripping components attached to, and extendingradially into, the frame. The components include a pointed shaft and acontact element having a serrated contoured contact surface. The pointof the shaft contacts and slightly enters the bone, thereby providing aforce against the bone coaxial with the shaft axis. The contact elementis adjustably mounted on the shaft and the angle of the contact surfaceis adjusted relative to the shaft axis so that the bone surface iscontacted by the contact surface. The contact element is secured againstthe bone to provide a force against the movement of the bone parallel tothe shaft axis. In this manner, a two-point suspension system isprovided that minimally contacts the exposed bone and minimallyinterferes with the area of the bone to be operated on.

The present invention further provides a prosthesis template for aidingin the determination of the desired position and orientation of aprosthesis relative to a bone. The prosthesis has an exterior surfacethat simulates the exterior surface of the bone and an interior surfacecomprised of one or more relatively planar surfaces to which theprepared bone must conform. The prosthesis template has a functionalinterior surface defined by at least three contour lines. Thisfunctional interior surface corresponds to the exterior surface of theprosthesis so that when the template is positioned near the bone itprovides a means for evaluating the position and orientation of theprosthesis exterior surface relative to the bone.

In accordance with additional aspects of this invention, the prosthesistemplate includes cut guide marks on the template. The cut guide markslie in the various planes that correspond to the interior surfaces ofthe prosthesis, and thus correspond to the bone cuts that must be madein order to prepare the bone for the prosthesis. The relationshipbetween the cut guide marks and the functional interior surface of thetemplate correspond to the relationship between the interior surface andthe exterior surface of the prosthesis. Thus, when the template ispositioned near the bone, it provides a means for evaluating theposition and orientation of the prosthesis interior and exteriorsurfaces relative to the bone.

In accordance with other aspects of this invention, the templateincludes rod alignment tabs positioned on the anterior side of thetemplate. A reference rod can be attached to the alignment tabs. In thismanner, the rod provides an additional reference between the position ofthe template and the longitudinal axis of the bone. Additionally, thetemplate includes mounting means for rigidly securing the templaterelative to the bone.

An additional object of the present invention is to provide anorthopedic saw guide for confining the blade of a surgical saw tomovement in a single plane while allowing translational and rotationalmovement of the blade within the plane. A pair of elongated guide platesare secured together at either end to form a partially enclosed space.The distance between the inner surfaces of the guide plates isadjustable, and is preferably adjusted to be slightly greater than thethickness of the specific blade to be used. Mounting means for rigidlysecuring the saw guide relative to the bone, so that the plane definedby the space between the inner surfaces corresponds to the out plane, isprovided.

In accordance with still further aspects of this invention, the innersurfaces of the guide plates include guide liners that are comprised ofa low-friction material. The liners may be permanently secured to theguide plates or removable and disposable. The guide plates are curved inthe plane of the guide surfaces so that the saw guide can be mountedclose to the end of a bone to provide maximum access to the bone withthe closest possible positioning of the guide.

In accordance with additional aspects of this invention, a stabilizingdevice is provided for creating a rigid link between the mounting memberand the reference structure, in addition to the link provided by themanipulator. Any compliance of the end of the saw guide is thusprevented so that, for example, the inner surface of the guide is heldrigidly within the cut plane throughout the cutting task. Thestabilizing device permits use of a smaller and more compact robot inthe surgical system.

In accordance with other aspects of this invention, the stabilizingdevice is incorporated into a safety feature of the task control means.When the mounting member, tool, stabilizing device, and the article towhich the stabilizing device is attached are made of electricallyconductive materials, the attachment of the mounting member to thestabilizing device produces a simple circuit. The task control meansdetects when the circuit is complete and will not allow manipulatormovement during that time. Thus, the robot will never inadvertently movewhen the mounting member Is stabilized.

In accordance with still further aspects of this invention, the templateand tools used in the system include a tool identification pattern thatuniquely identifies each tool. An identification device is included inthe attachment means so that when the template or tool is mounted, theidentification pattern can be read and transferred to the task controlmeans. The identification is then compared to the identification for thetemplate or tool that is appropriate for the task. An error message isgenerated and displayed if the incorrect template or tool is attached.

In accordance with still other aspects of this invention, the robot baseincludes a tiltable safety stand, including a means of communicating tothe task control means the status of the stand. The safety stand isconfigured so that if the robot encounters a rigid object while it ismoving, the stand will tilt away from the object, thereby preventing thecontinued force against the object. When the stand tilts, a safetysignal is generated that is received by the task control means and isindicative of the need to shut off the power to the robot.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an isometric view of a prosthesis and a bone, with the end ofthe bone prepared to receive the prosthesis;

FIG. 2 is a side view of a bone with a prosthesis press fit thereon,with the bone partially cut away to show the prosthesis anchoring stud;

FIG. 3 is a pictorial view of the system of the present inventionincluding a patient positioned on an operating table;

FIG. 4 is an isometric view of the bone immobilization device of thepresent invention with a representative femur suspended by the device;

FIG. 5 is a side view of the bone immobilization device with the frameand fixation components shown adjusted to a raised position relative tothe base of the device;

FIG. 6 is an exploded view of one fixation component of the boneimmobilization device;

FIG. 7 is an isometric view of a robot used in the system illustrated inFIG. 3;

FIG. 8 is an isometric view of the robot illustrated in FIG. 7 showingthe movement capabilities of the robot;

FIG. 9 is an isometric view of the wrist and the mounting flange of therobot with the tool-coupling device of the present invention explodedaway from the mounting flange;

FIG. 10 is an isometric view of the wrist and coupling deviceillustrated in FIG. 9 with a sample tool attachment flange shownexploded away from the coupling device;

FIG. 11 is an isometric view of the robot safety stand used in thesystem illustrated in FIG. 3;

FIG. 12 is a side view of the robot safety stand with portions of theupper plate and one spring assembly cut away to show the compliancefeatures of the stand;

FIG. 13 is a top view of the top plate of the robot safety stand to showthe configuration of the upright supports and the spring assemblies;

FIG. 14 is a block diagram of the robot and peripherals, controller, andsupervisor of the system of the present invention;

FIG. 15 is an isometric view of a use of the prosthesis template of thepresent invention attached to the robot and positioned near animmobilized bone;

FIG. 16 is an isometric view of the template illustrated in FIG. 15;

FIG. 17 is a side view of the template attached to the robot andpositioned near the end of an uncut bone;

FIG. 18 is a top view of the template with the top portion cut away toshow the relationship between the horizontal plate and an uncut bone;

FIG. 19 is an isometric view of a use of the saw guide of the presentinvention positioned near the immobilized bone;

FIG. 20 is an exploded view of the saw guide;

FIG. 21 is a top view of the saw guide with a saw blade positionedbetween the guide plates;

FIG. 22 is a front view of the saw guide;

FIG. 23 is a side sectional view of the saw guide illustrated in FIG. 21with a section taken along line 23 and a saw blade positioned betweenthe guide plates;

FIG. 24 is an isometric view of a use of the drill guide of the presentinvention positioned near the immobilized bone;

FIG. 25 is a flow diagram of the method of the present invention fordetermining the desired position and orientation of a prosthesisrelative to a bone;

FIG. 26 is a flow diagram of the method of the present invention fordetermining the position and orientation of a saw guide relative to thedesired position of the prosthesis; and

FIG. 27 is a flow diagram of the method of the present invention fordetermining the position and orientation of a drill guide relative tothe desired position of the prosthesis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to a system and method for aiding in asurgical procedure that includes the task of determining the preciseposition and orientation of a tool relative to a reference structure orpoint. That determination may be in part a geometrical solution and inpart a subjective solution based on the physiology of the patient. Thesystem will be described in terms of a total knee arthroplasty (TKA),which is a representative procedure having the above-describedcharacteristics. For illustration, the replacement of the distal end ofa femur will be described. The below-described system and method areapplicable to similar surgical procedures. It is to be understood thatthroughout the present application, the use of the term "position"describes both point and orientation information. This is acceptedterminology in the area of robotics.

In one preferred embodiment, the present invention provides a two-stepmethod and related apparatus for aiding in surgical procedures. Thefirst step includes the determination of the desired position of asurgical task relative to a bone. In the TKA, the surgical task includesreplacing a portion of the bone with a prosthesis. The surgeon isprovided with a template having a feature that represents a portion ofthe prosthesis, such as the prosthesis exterior surface. The surgeonpositions the template such that the template feature is in the desiredposition of the corresponding prosthesis portion, and then causes thetemplate position relative to a fixed point to be recorded. The secondstep, or bone preparation step, includes determining the position of atool, e.g., a saw guide or drill guide, relative to the desiredprosthesis position. This step also includes actually positioning thetool. A tool position is determined by combining the position of thetemplate with geometric information defining the task; i.e., theprosthesis' characteristics defining the manner in which the bone mustbe prepared. For example, by determining the position of the anteriorcut from the position of the template, the position of the saw blade isalso determined; i.e., the blade must be held by the saw guide in theplane of the cut near the bone. This method provides a clear distinctionbetween the prosthesis-positioning step and the bone-preparation step.

With reference to FIGS. 1 and 2, a prosthesis 10 is used to replace theend of a bone 12 when the bone is damaged or diseased in some way, or ismalaligned within the knee joint. The bone 12 may be a femur with theprosthesis 10 fitted onto the distal end 14. Other identifiable portionsof the bone are the anterior side 16, the posterior side 18, thecondyles 20 and 21, and the notch margin 22. The exterior surface 26 ofthe prosthesis simulates the distal end of a normal femur, including thecondyles and the notch margin.

With respect to gross alignment, the femoral position relative to theknee joint is important. The translational degrees of freedom of thefemur are the distal-proximal, anterior-posterior, and medial-lateraldirections. Rotations about these axes are referred to as axial,varus-valgus, and flexion-extension, respectively. Femoral prosthesisgross alignment errors include: (1) distal-proximal positioning error,which causes excessive tightness or laxity in the tendons of the kneewhen the knee is extended; (2) anterior-posterior positioning error,which causes misalignment of the mechanical axes of the femur and tibia;(3) flexion-extension rotation of the prosthesis, which results inexcessive flexion or extension of the joint; and (4)varus-valgusrotation of the components, resulting in a knock-kneed or bow-leggedeffect or the tibial and femoral components meeting in shear. Becausethere is no exact femur model to follow, and the natural distal end ofthe femur may not provide a good model, the correct gross alignment ofthe prosthesis is highly dependent upon the surgeon's subjectiveevaluation of the knee.

With respect to local fit, the preparation of the femur for theprosthesis is dictated by the configuration of the interior surface 28of the prosthesis. The geometric relationships that define the bonepreparation tasks are the same as the geometric relationships making upthe interior surface. The interior surface of the prosthesis is made upof anterior 30, posterior 32, and distal 34 planar surfaces, andchamfers 36 and 37, which are slightly curved. Additionally, twoanchoring studs 38 and 39 extend normally from the distal surface 34. Inorder to prepare the bone, planar cuts are made on the femur thatcorrespond to the interior surfaces of the prosthesis. These cuts resultin anterior 40, posterior 42, distal 44, and chamfer 46 and 47 planarsurfaces on the femur. The chamfer cuts 46 and 47 can be single-cutplanes that provide a relatively tight fit with the curved surfaces 36and 37 of the prosthesis. Alternatively, multiple chamfer cuts can bemade to produce more rounded cut surfaces. Also, stud holes 48 and 49are drilled to receive the anchoring studs 38 and 39, respectively.

With reference to FIG. 2, after bone preparation, the prosthesis ispressfit onto the femur. The cut surfaces of the bone contact theinterior surfaces of the prosthesis.

For each manufacturer, bone type, and size, the configuration of theprosthesis can be determined by taking simple physical measurements. Thepresent system integrates these known geometric relationships betweenthe interior surfaces of the prosthesis with the subjectivedetermination of the surgeon as to the desired gross alignment of theprosthesis.

With reference to FIG. 3, one preferred embodiment of the system of thepresent invention utilizes an operating table 50, a bone immobilizationdevice 52, a robot 54, a robot controller 55, and a robot supervisor 56.The patient is positioned so that the femur is supported and rigidlysecured within the bone immobilizer. In practice, proximal femurdisplacement is prevented by placing sandbags or a secure belt over thehips of the patient. The immobilizer is attached to the operating tableby the immobilizer base, not shown. Thus, throughout the TKA, the femurposition is fixed in relation to the operating table 50.

The robot is rigidly attached to the operating table 50 by robot safetystand 65. The operating table thus provides a reference structure forthe positional relationship between the femur and the robot. In apreferred embodiment, a tool attached to a robot mounting flange thatextends from the robot manipulator can be moved relative to the base, inany of the six degrees of freedom. With this system configuration, atool connected to the mounting flange can be accurately positioned aboutthe immobilized femur. The robot includes position-sensing means forgenerating signals indicative of the position of the mounting flangerelative to a world coordinate system fixed with respect to the robotbase.

The robot controller 55 directly controls and monitors the movement ofthe robot. The robot and its peripherals are connected to the controllerby input/output cables 58a and 58b, and communications cable 59. Theinput/output cables 58 and communications cable 59 are connected toinput/output port 60 and communications port 61, respectively. Movementcommands are generated by the controller and sent to the robot viacommunications cable 59. Mounting flange position signals are receivedfrom the robot over communications cable 59, and processed by thecontroller. Monitoring and control of robot peripherals, such as thesafety stand, are also carried out by the controller. Such peripheralsare connected to the controller by input/output cables 58 viainput/output port 60.

In one preferred embodiment, the robot supervisor 56 supervises thecommunications between the robot and the controller. The supervisor inthe illustrated embodiment includes a personal computer (PC) 66 (shownin reference) and display device 67. The PC houses the robot supervisoryprograms and the system data. The supervisor may enhance the operationof the system by providing a simplified operator interface. The surgeoncan then control the system without having to understand the robotcommand language utilized by the controller. The controller is connectedto the supervisor by communications cable 62 that extends between thecontroller's supervisor port 63 and the supervisor's communication port64 (both shown in reference). The robot controller and supervisor can becovered with a sterilized shroud during the operation and still beeasily manipulated.

As noted above, the TKA is divided into two steps. In the first step,the desired spatial relationship between the prosthesis and the distalend of the femur is established. In one preferred embodiment, this stepis accomplished by means of a prosthesis template that is attached tothe robot mounting flange. Generally, the template includes a feature,such as a surface, a bore or a pointing member, that can be used torepresent a task position that is relevant to the performance of a bonealteration task. For replacing the distal end of the femur with aprosthesis, the template feature preferably comprises a surface thatcorresponds to an outer surface of the prosthesis. When the templatefeature is placed in a desired position relative to the desired positionof the prosthesis surface, then the template position, termed thereference position, is stored in the system database. In one preferredembodiment, the surgeon manually positions the template near the femur.Once the template position is correct, the robot arm is locked and theposition of the template in the world coordinate system is recorded.

The second step of the TKA comprises the bone alteration tasks ofcutting and drilling the femur in preparation for the prosthesis. Inthese tasks, surface cuts will be made by a surgical saw, and stud boreswill be drilled by a surgical drill bit. The supervisory programcombines the reference position with a geometric database to generatecoordinate data for each cutting and drilling task. The geometricdatabase describes the planes and axes in which the saw guides and drillguides, respectively, must be aligned to perform the specified bonealterations. A program is generated to command the robot to move thetool attached to the mounting flange to the proper position so that thetool is in place for the specific task. Once the tool is positioned, therobot arm holds the tool while the surgeon carries out the sawing ordrilling task.

After the bone is prepared, the prosthesis is placed on the bone end.Because of the geometric exactness provided by the robot system, bonecuts and bores are achieved that allow for an accurate press-fit of theprosthesis onto the bone end.

Referring now to FIG. 4, one preferred immobilizer to be used with thepresent system includes base 68, bone-positioning frame 70, and bonefixation components 72. In one preferred embodiment, a tool-stabilizingdevice 73 is attached to the immobilizer. The stabilizing device will bediscussed below. Although the full femur is shown, in an actualprocedure, only a small portion of the distal end of the femur would beexposed. The tibia, kneecap, ankle, etc., would be beside or below thefemur in the foreground of FIG. 4.

The immobilizer base 68 connects the immobilizer to the operating table50. The base includes sliding plate 74, base clamp 76, upright 78 (shownin reference) and upright clamp 79. The sliding plate includes bolts 82and washers 83 to secure the plate onto the operating table. The boltsextend through channels 84 and threaded table runs 85. The immobilizerposition can thus be adjusted relative to the table, both side to sideand end to end. The position is secured by tightening the bolts 82 inthe runs 85.

The base clamp 76 is hollowed to slidably receive upright 78. The heightand rotational position of the immobilizer is adjusted by looseningscrews 86 in the base clamp, thereby loosening the grip of the clamp onupright 78. Once the upright is adjusted to the desired position, thescrews are tightened, thereby compressing the base clamp against theupright in secured relationship.

The upright 78 is preferably an integral part of the upright clamp 79.The upright clamp extends vertically as clamp flanges 90. Attachmentcylinder 92 extends through and between the clamp flanges. Set screws 93are positioned in the flanges normal to the attachment cylinder. Therotations/position of the attachment cylinder is secured by tighteningthe set screws 93 into the flanges and against the attachment cylinder.

The bone-positioning frame 70 is made up of semicircular upper frame 94and lower frame 96. Lower frame 96 includes frame tab 98, connectingledges 100, and anchor pins 101 (discussed below). The frame tab 98extends centrally from the lower frame. A bore runs through the frametab and is shown in reference. The frame tab is split from the bore tothe bottom of the tab. Bolt 102 connects the lower portions of the splittab and can be tightened to reduce the bore diameter. The frame tab iscoupled to the frame clamp by attachment cylinder 92 which extendsthrough the tab bore. The angle of the frame relative to the base plateis adjustable by rotating the frame over the attachment cylinder. Oncethe desired frame angle is achieved, bolt 102 is tightened to secure thetab against the attachment cylinder. Thus, the angle of the frame isadjusted by loosening either the bolt 102 or the pair of set screws 93,to allow the frame or the attachment cylinder, respectively, to rotate.

The upper frame 94 includes projections 106. The upper frame isconnected to the lower frame by the securing of projections 106 to theledges 100 by screws 108. The upper frame is thus readily removable fromthe lower frame for ease of positioning the bone within or removing thebone from the immobilizer.

The frame includes a plurality of threaded radial bores 110 spaced alongthe frame edge. The fixation components 72 of the immobilizer extendthrough the bores. Once the bone is positioned through the frame, andthe knee joint exposed, the fixation components are tightened to thefemur and to the frame edge to hold the femur in place.

It is preferable to grip the exposed bone rather than the skin or othertissue. Since the posterior portion of the knee is not generally widelyexposed, the fixation components will typically be situated in the upperportion of the frame so as to be in a position to contact the exposedanterior portion of the femur. Thus, the majority of the bores 110 arepositioned in the upper area of the frame. Alternatively, if other bonesare being operated on, it may be preferable to have the fixationcomponents enter the bone from the posterior side. In such a case, theframe bores 110 are positioned about the lower frame 96. Additionally,if the fixation components are both positioned through the upper frameor both through the lower frame, then the upper frame can be removedfrom the lower frame while the bone remains secured to one half of theframe by the fixation components.

As shown in FIG. 5, the bores 110 through the frame do not lie withinthe plane of the frame, but are set at an angle. The angling of thebores allows the fixation components to extend back and away from thearea of the operation, thereby allowing maximum access to the bone. Inthis manner, the end of the femur is approachable by the surgeon fromalmost any angle and complete surface cuts can be made withoutrepositioning any part of the immobilizer.

The immobilizer provides six degrees of freedom for positioning thebone. Translational freedom is provided by adjusting the sliding platealong the channels 84, and runs 85, and by adjusting the height ofupright 78 within base clamp 76. Rotational adjustments are provided byrotation of the upright 78 within base clamp 76, rotation of the frame70 about attachment cylinder 92, and rotation of the fixation componentsabout the frame 70; i.e., by repositioning the fixation componentsrelative to the frame by using a number of bores 110.

With reference to FIG. 6, one preferred fixation component is a coactinggrip 116. A pair of grips are adequate to rigidly secure a bone withinthe bone immobilization device. Each coacting grip 116 includes athreaded shaft 118, a contact washer 120, a point 126, a washer nut 128,a frame nut 130, screw nut 131, and a screw head 132. The contact washeris preferably wedge shaped and has a serrated contact surface 134. Ashaft bore 136 extends through the contact washer, relatively normal tothe contact surface. The bore is oversized so that the angularrelationship between the contact surface and the shaft is adjustable byrocking the washer about the shaft. In one preferred embodiment, avariety of contact washers are available, the washers beingdifferentiated by the contours of their respective contact surfaces. Thecontact surfaces range from a flat surface to a concave surface. Thespecific contact washer for each coacting grip is chosen during theoperation so that the contact surface closely conforms to the bonesurface against which the washer will be tightened.

The point 126 is attached to the shaft by set screw 138 inserted throughbore 139 against the point. Alternatively, the point 126 may be anintegral part of the shaft.

In use, the pointed shaft 118 is threaded through a bore 110 in theframe. The portion of the shaft in the interior of the frame is threadedwith the washer nut 128 and extended through the contact washer 120. Theshaft position is adjusted until the point 126 slightly penetrates thebone. On the outside of the frame, the frame nut 130 is then screwedonto the shaft and tight against the frame to secure the shaft relativeto the frame. The contact washer 120 is then adjusted about the shaft sothat the contact surface 134 contacts as much bone surface as possible.The washer nut 128 is then tightened down to hold the contact element incontact with the bone. The teeth of the serrated contact surfaceslightly penetrate the bone to prevent slippage. The screw head, screwedagainst screw nut 131 and attached by set screws 140 to the shaft,provides a gripping surface to be used in the shaft-adjusting process.The tightening of the two coacting grips generally takes placesimultaneously.

The coacting grips 116 are capable of suspending the femur withoutsupport from below. The suspension is achieved by the coacting forces ofthe shaft points and contact washers. Each shaft point provides a forceagainst the bone that prevents the bone from moving in directionsperpendicular to the axis of the shaft. Each contact washer provides asurface force against the bone that prevents the bone from moving indirections parallel to the shaft. This two-point suspension methodreduces interference with the femur end as well as damage to the bone.

The immobilizer 52 can be used in a variety of operations where it isdesirable to rigidly immobilize a bone throughout a procedure. Once thebone is immobilized, the operation can proceed. The next step of thepresent invention is to teach the robot the desired position of the bonealteration task.

Desirable characteristics of a robot used in the present system includethat the robot be capable of moving a tool mounted to the robot in sixdegrees of freedom; that the mounting flange be capable of gripping oradaptable to grip a variety of surgical tools; that the robot has a highrepeatability of mounting flange positioning; and that certain safetyfeatures be available on, or integratable into, the robot and controlsystem. With reference to FIG. 7, one suitable robot 54 is the PUMA 200robot available commercially through Unimation. The PUMA 200 robot isrelatively small, and thus will fit readily into a surgical area and canbe mounted directly onto or adjacent an operating table. The robot isrigidly mounted in relation to the immobilizer device by securing therobot directly to the operating table or to a safety stand 62 which, inturn, is mounted on the operating table.

The robot 54 includes a trunk 142 extending from a base 144, a shoulder146 connecting the trunk to an upper arm 148, an elbow 150 connectingthe upper arm to a lower arm 152, and a wrist 154, attached to the lowerarm, from which extends a mounting flange 156. The section of the robotthat includes movable parts is referred to as the manipulator. Themanipulator includes permanent-magnet DC servomotors for driving therobot movement. Incremental optical encoders for determining manipulatorposition relative to a fixed point on the base robot, and fordetermining manipulator velocity, are included in the joints. Theencoders convert positional data into electrical signals. Generally, theposition of each section of the manipulator is combined to determine theposition of the mounting flange or a tool attached to the mountingflange. When the robot is not in use, the wrist rests in nest 157.

With reference to FIG. 8 in conjunction with FIG. 7, the manipulator iscapable of moving the mounting flange 56 in six degrees of freedom. Therobot rotates about the vertical trunk. The upper arm is raised andlowered by rotation about the shoulder. The lower arm raises and lowersthe wrist by rotation around the elbow. Finally, the wrist rotates aboutthree axes defined by the longitudinal axis of the lower arm, the wrist,and the center of the mounting flange.

Attachments to the mounting flange, such as mechanical grippers orelectronic sensing devices, are available from the robot manufacturer orfrom other manufacturers specializing in such attachments. Withreference to FIG. 9, the standard mounting flange provided on the PUMA200 robot has screw holes 158 positioned about the perimeter of theflange. The flange also includes an alignment pin 159 that is used toensure repeatable positioning of tools on the flange. The present systemutilizes a coupler 160 that connects to the mounting flange 156 andcouples various tools to the robot wrist. The coupler includesconnecting plate 162, coupling block 164, identification component 166,signal port 168, connecting bore 170, and alignment studs 172. Theconnecting plate alignment bore (not shown) is positioned so as to matchwith the mounting flange alignment pin 159. The plate is secured to themounting flange by screws 173 extending through plate bores 174 to screwholes 158. The coupler is fixed on the mounting flange for the durationof the surgery. In this manner, the position of the coupler componentsare fixed relative to the robot mounting flange.

The coupling block 164 is perpendicular to and offset on the connectingplate. Tools are attached directly to the coupling block during theoperation. Each tool has an attachment flange, an example of which isshown in FIG. 10, that mates with the coupling block. The flange 175includes a thumbscrew 176 that extends through the flange into theconnecting bore 170. The flange also includes a pair of bores 178 thatmate with the alignment studs 172. Each tool includes a similarattachment flange and is precisely and repeatably mountable on thecoupling block. The position of each tool relative to the position ofthe mounting flange is thus known when the tool is mounted. Thisrepeatable mounting capability allows the robot to be taught themounted-tool configuration in a simple manner.

It is standard practice in robotics to direct robot movements in termsof tool positions. This is done by first teaching the robot a tooldefinition. A tool mounted on the mounting flange is described to therobot as a single point that is offset from and oriented relative to therobot mounting flange. A common point used for defining a tool is thetip of the tool or some similar point remote from the attachment flange.A common robot control function accepts an array of values that definesthe tool point relative to the mounting flange. Tool positioningcommands can then be utilized. The robot control functions includeimplicit transformations from a tool position in a coordinate system toa robot mounting flange position. Given a movement command, the robotwill move the robot mounting flange so that the tool point is at thecommanded position.

The efficiency of the present system is increased by the inclusion of anidentification component 166 on the coupling block. This component isused to identify the tool attached to the robot. This identification isthen compared to an identification code stored in the control memorythat corresponds to the tool required for the task at hand. For example,the identification code for the saw guide will satisfy the toolidentification test that is run during the bone-cutting steps of theprocedure. The identification component is used as a safeguard againstthe attachment of an incorrect tool. Additionally, it is a time-savingdevice in that the robot controller indicates to the surgeon immediatelythat an improper attachment has taken place so that time is not wastedin identifying a tool attachment error and correcting it during theoperation.

In one preferred embodiment, the identification component is comprisedof five phototransistors 180 arranged in a pattern along the surface ofthe coupling block. Each phototransistor is an emitter and receiver pairand is capable of transmitting and receiving an infrared signal. Eachphototransistor is connected to the signal port 168 by a wire (notshown) suitable for carrying a signal. Signal port 168 is connected tothe controller by input/output cable 58a. Radiation emitted from eachphototransistor is detected by the respective receiver if it isreflected back; i.e., if a surface is positioned slightly above thesensor to thereby cause the light to reflect back. If no surface ispresent, or one lies flush against the sensor, then no reflected lightis detected. Thus, the signals sent by the phototransistors to thecontroller might be interpreted digitally as 1's and 0's for reflectedand nonreflected signals, respectively. The output of the sensors iscollectively read as a binary word. Thus, 32 different identificationcodes are represented by the five sensors. The corresponding toolattachment flange surfaces are patterned with slight bores. One patterncorresponds to each tool. On the sample flange 175 the identificationpattern 181 will be flush against the phototransistors on the couplingblock when the flange is attached. The pattern 181 includes three areasthat are slightly bored so as to provide a means for reflecting lightemitted from the phototransistor back onto the coupling block. No lightwill be reflected from the other two phototransistors because theattachment flange will be flush against the phototransistors. Thus, theidentification for the tool corresponding to the sample attachmentflange is some combination of three 1's and two 0's, the combinationdepending upon the order in which the signals are read. During the TKA,a continuous signal is passed between the controller and thephototransistors. The return signal is read by the controller at thetool mounting step and the identification code determined by the controlprogram.

With reference to FIG. 11, the robot safety stand 65 includes top plate182, base plate 183, support legs 184, and spring assemblies 185. Thebase 144 of the robot is secured to the top plate 182 by screws 186. Thebase plate in turn is secured to the operating table 50 by screws 187.In this manner, the robot position is stable relative to the operatingtable.

Although the robot is preferably programmed to move slowly, so thatthere is little chance of an accident occurring due to the robotstriking an object at a high speed, there is still a chance that therobot may encounter a rigid object while it is moving. If such anincident occurs, power to the manipulator should be cut off immediately.In one preferred embodiment, the force of the robot against a rigidobject will cause the top plate to tilt away from the base plate. Thecompliance of the stand prevents the robot from damaging the object andprovides an indication to the controller over cable 58b that the powershould be automatically shut off. Since the PUMA 200 robot is relativelylightweight, a great deal of force need not be applied by the robot to arigid object in order for this power-down situation to occur.

As illustrated in FIG. 12, a support leg includes upright 188 and ballbearing 189. The ball bearing is captured between the upper portion ofthe upright and lower side of the top plate which is slightly indentedto receive the ball bearing. Adjacent each upright is a contact switch190 attached to the lower side of the top plate. The upright and contactswitch are made of electrically conductive materials and form a simpleground loop detection circuit. The contact switch is positioned so thatwhen the top plate rests on the ball bearing and upright, the contactswitch completes the circuit. Each upright is connected to a wire, notshown, and the wires are bundled into cable 58b and connected to therobot controller input/output port 60. During periods of robot movement,the controller continuously polls the circuits to check for a break inthe continuity between a switch and an upright. When this occurs, powerto the robot is immediately shut off.

Each spring assembly 185 includes a spring 193, a casing 194, and aspring mount 195. The spring mount extends downwardly from the lowerside of the top plate and includes a securing flange 196 on theunconnected end. The spring wraps around the spring mount and is securedon the mount by securing flange 196. The spring and mount are encased incasing 194 which is hollow and extends upwardly from the upper side ofthe base plate. When the top plate rests on the support legs, thesprings are slightly compressed within the casings, thereby providing adownward force against the top plate and an upward force against thebase plate. In this manner, a firm base is established for the robot.

With reference to FIG. 13, the support legs and spring assemblies arepositioned between the plates so that the tilting of the top plate inany direction will result in at least one contact switch losing contactwith an upright. When the top plate is tilted, the spring mount in thespring assembly, or assemblies, attached to the portion of the top platetilting away from the base plate will slide upwardly and away from thecasing by a compression of the spring. In this manner, the platescontinue to be connected by the spring assemblies so that the robot doesnot topple from the stand.

Referring now to FIG. 14, the robot is controlled by controller 55 thatis available through the robot manufacturer. The PUMA 200 controllerincludes a Digital Equipment Company (DEC) LSI-11 computer 198 whichincludes a processor, memory, and communications board. Thecommunications board includes robot-communications port 61, input/outputport 60, and supervisor port 63. The robot is also provided with a teachpendant, an input device, such as a keyboard, and a display device, suchas a terminal display screen, all shown in reference.

In the PUMA 200 controller, the control programs are stored in aComplementary Metal Oxide Semiconductor (CMOS) nonvolatile memory. Therobot commands and feedback are routed through the robot-communicationsport 61. The input/output port 60 is a programmable control output thatis actuated by the control programs. A variety of peripherals, such asthe safety stand and tool identification device can be attached throughthe input/output port.

The PUMA controller is provided by the manufacturer with its ownoperating system/robot control language known as VAL-II (VersatileAssembly Language). Programs are written in VAL-II to control themovement of the robot. The programs include: robot-control programs fordirectly controlling the robot with motion instructions; process-controlprograms that run parallel to the robot control programs for monitoringand controlling external processes via lines connected to theinput/output port; and system programs for system operation. Theprograms are stored in the controller memory and processed by thecontroller. A sampling of the VAL-II commands and functions used by thepresent system to implement robot movements is listed in TABLE I.

                  TABLE I                                                         ______________________________________                                        Name                Description                                               ______________________________________                                        MOVE <location>     Moves the robot to the                                                        position and orientation                                                      described by "location."                                  SET <location variable>                                                                           Sets the left variable equal to                           =<location variable>                                                                              the right variable.                                       HERE <location variable>                                                                          Sets the value of a                                                           transformation or precision                                                   point equal to the current                                                    robot location.                                           TOOL {<compound>}   Sets the value or definition of                                               the tool transformation equal                                                 to the transformation value                                                   given.                                                    SPEED (<expression>)                                                                              Returns one of the speed                                                      values used by the system.                                                    The value is always a                                                         percentage of "normal" speed;                                                 i.e., SPEED 100.                                          APPRO <location>, <distance>                                                                      Moves the tool to the position                                                and orientation described by                                                  "location," but offset along                                                  the tool Z-axis by the                                                        distance given.                                           DISTANCE (<compound, compound>)                                                                   Returns the distance in mm                                                    between the points defined by                                                 the two specified transforma-                                                 tion values.                                              NEST                Moves the robot into its nest.                            ______________________________________                                    

There are several methods for controlling the movements of the robot.The robot is equipped by the manufacturer with a teach pendant (notshown) that can be connected to the input/output port 60 of thecontroller. The teach pendant is a hand-held device for interactivelymaneuvering the robot. The teach pendant is generally used to maneuverthe robot through a series of steps making up a path. The controllerrecords points along the path so that the robot can then repeat thesteps under the controller's guidance. A joystick, voice control device,or other movement indicator provide suitable methods for controllingrobot movement interactively. These methods are contrasted with themethod wherein the controller processes a program written in VAL-II thatis stored in the controller memory or passed from a supervisor. As theVAL-II program is run, the robot moves through the programmed steps. Therobot can also be placed in a passive mode wherein the manipulator ismanually moved; i.e., by an operator actually grasping and moving themanipulator through a recordable path. In this mode, the servomotors aredisabled while the encoders remain active. All of the other modes arereferred to as active modes. In these modes, both the servo motors andencoders remain active.

The robot is capable of recognizing and operating within two coordinatesystems: a world coordinate system and a tool coordinate system. In theworld coordinate system, the origin of the system is at the shoulder orsome other point of the robot which remains fixed relative to the base.In the present system, the origin is fixed relative to the operatingtable and to the patient's bone. The robot can be programmed to move anattached tool to any world coordinate position.

In the tool coordinate system, the origin defaults to a point on therobot mounting flange that moves with the flange. The default origin canbe replaced by an origin related to, and more useful for, a specifictool attached to the flange. The tool coordinate system moves with themounting flange as it is moved by the robot. Each tool can be defined bytool data points in the tool coordinate system. As described in greaterdetail below, the data representing a tool definition is combined withthe template reference position and with a geometric database describingthe prosthesis to determine the position of the tool, e.g., a saw guide,for each task.

The robot controller has a supervisor port into which a supervisor canbe connected. Information describing and aiding in the implementation ofthe supervisory-communications interface is provided with the controllerby the robot manufacturer. The supervisor 56 may include a personalcomputer (PC) 66 and a display device 67. The PC includes a centralprocessing unit (CPU), input/output ports, and memory. In one preferredembodiment, a PCs Limited 386, an IBM-compatible personal computermanufactured by Dell Computer Corporation, connected to a color-displaydevice, is used as the supervisory system. The PC is connected to thecontroller's supervisor port 63 through the PC's COM2: serial port viacable 62. Through this connection, programs run on the PC supervise therobot controller. The supervisor provides data as well as controlcommands and programs in the VAL-II language. Although a supervisor isused, all robot movement commands are preferably routed through thecontroller to the robot.

A touch-screen input system is used so that the monitor and the inputdevice are integrated. Personal Touch Corporation's Electronic InputScreen, available under the trademark Touch Window, is fixed to thefront of the display device and used as the command input device duringthe operation. Such an input screen is highly desirable in a surgicalenvironment in that it can be draped with a transparent sterilizedshroud and still be easily manipulated by the surgeon. The bonealteration control program provides large squares displayed on themonitor that correspond to specific commands. The screen areaimmediately in front of the display square corresponding to the desiredcommand is simply touched by the surgeon to indicate the command choice.The use of the touch-screen input system eliminates the need for otherinput and display devices, such as the teach pendant and keyboards,during the TKA. However, during system programming and data entry,either the supervisor or controller keyboard is used to inputinformation.

While, in one embodiment of the system of the present invention, the TKAprogram is implemented using only the controller, the addition of thesupervisor in an alternative embodiment increases the capabilities ofthe overall system. For ease of description, the system will bedescribed with the supervisor acting as the main processor. However, itis understood that in alternative embodiments, the controller is used toperform additional or all processing functions.

By using the supervisor, a programming language that is more specific tobone alteration surgeries, and easier to implement than the VAL-IIlanguage, is implemented. Preferably, a high-level English-like languageis used so as to increase the ease of using the system by those who arefamiliar with such surgeries, but may not be familiar with the VAL-IIlanguage or computer programming in general. Existing languages, such asBASIC, can be used, or others can be developed for the specific purpose.Any program downloaded from the supervisor to the controller is writtenin the VAL-II language so that the controller can process the programand generate movement commands.

In the present system, the high-level language program generates aVAL-II program. The VAL-II program calls a library of VAL-IIsub-programs. The subprograms, in turn, call a set of VAL-II primitives.It is the set of primitives that command the robot movements. The use ofa high-level language to write the robot control programs in VAL-II isanalogous to using a high-level language to generate an assemblylanguage. In the latter instance, a program written in the high-levellanguage, such as BASIC or C, is compiled to create a meta-code. Themeta-code is linked to a function library to include the functionsreferenced by the program into the meta-code. A second linking operationis performed to create the assembly language program. These steps arecommon in the area of programming with high-level languages.

By establishing a program in a high-level language, the program can betailored to the application. In the present system, the program for thebone alteration surgical procedure is directed to template positioning,and bone cutting and boring. Thus, the high level language onlyreferences those VAL-II programs that are necessary to perform thesetasks. Preferably, simple operator commands, such as "DO DISTAL CUT,"generate, through the process described above, the VAL-II primitivesdirecting the movement of the robot to carry out the task. The surgeonis spared from making any more detailed programming decisions when ahigh-level language is used. A skeleton of a sample custom surgical taskdescription language will be used in the present description as anillustration.

Two tasks must be carried out prior to using the robot system:establishing a descriptive geometric database for the prosthesispreparation task; and developing programs in VAL-II and a high-levellanguage that describe and direct the procedures. In one preferredembodiment, geometric databases are established that describe, for eachprosthesis, the geometric relationships between the prosthesis and thebone-cut planes and bore axes necessary to prepare the bone for theprosthesis. Preferably, to establish the database, a program is run to:accept a high-level language script describing the geometry of aprosthesis interior surface; check the geometry for consistency; andproduce a machine-readable database file for use by other programs. Thedatabase program utilizes geometric primitives that are recognized bythe VAL-II language. The geometric primitives are the basis for therobot-movement commands. The primitives are established as

POINT--consisting of a triplet (x, y, z) or a name;

LINE--consisting of two points, or a name;

EDGE--which is a line bound to a plane;

PLANE--consisting of two or more lines; and

TEMPLATE--consisting of planes, lines, and points.

Using these primitives, a line can be defined by two points, and a planecan be defined by two lines. The template is defined by the five planes:anterior, posterior, distal, and two chamfer; and the two lines for themedial and lateral bores. For each plane, one line is specified as theAPPROACH EDGE so that the robot will move a tool to the plane from aspecific position and orientation within that plane. The geometricprimitives can be defined in terms of other primitives referenced byname, with the exception of a template that is self-contained. Using thestructured prosthesis definition, two prosthesis geometries that arerelated and differ only in scale can be defined by the same script bychanging only the lowest level, point (x, y, z), definitions to suit thedifferent sized component. The geometries are described in a coordinatesystem wherein the origin is some fixed point on the template. When thetemplate is actually used to determine the desired prosthesis position,and its world coordinate position is established, all of the data in thegeometric database can be transformed to represent points in the worldcoordinate system.

A database file is built for each prosthesis. A sample of a prosthesisdata entry script is listed in Table II.

                  TABLE II                                                        ______________________________________                                        FILENAME: "Type A"     #Type A Task (prosthesis)                              # define free lines a through f to serve as plane boundaries                  POINT end.sub.-- 1a OF LINE line.sub.-- a IS -1.0, -1.0401, 1.7266            POINT end.sub.-- 2a OF LINE line.sub.-- a IS 1.0, -1.0401, 1.7266             POINT end.sub.-- 1b OF LINE line.sub.-- b IS -1.0, -9898, .8561               POINT end.sub.-- 2b OF LINE line.sub.-- b IS 1.0, -9898, .8561                PQINT end.sub.-- 1c OF LINE line.sub.-- c IS -1.0, -.6000, 5089               POINT end.sub.-- 2c OF LINE line.sub.-- c IS 1.0, -.6000, .5089               POINT end.sub.-- 1d OF LINE line.sub.-- d IS -1.0, .6000, .5089               POINT end.sub.-- 2d OF LINE line.sub.-- d IS 1.0, .6000, .5089                POINT end.sub.-- 1e OF LINE line.sub.-- e IS -1.0, .8682, .7513               POINT end.sub.-- 2e OF LINE line.sub.-- e IS 1.0, .8682, .7513                POINT end.sub.-- 1f OF LINE line.sub.-- f IS -1.0, .8883, 1.0211              POINT end.sub.-- 2f OF LINE line.sub.-- f IS 1.0, .8883, 1.0211               # now define the planes                                                       EDGE proximal.sub.-- edge OF PLANE anterior.sub.-- plane IS LINE              line.sub.-- a                                                                 EDGE distal.sub.-- edge OF PLANE anterior.sub.-- plane IS LINE                line.sub.-- b                                                                 EDGE anterior.sub.-- edge OF PLANE anterior.sub.-- chamfer.sub.-- plane       IS EDGE                                                                       distal.sub.-- edge OF PLANE anterior.sub.-- plane                             EDGE posterior.sub.-- edge OF PLANE anterior.sub.-- chamfer.sub.-- plane      IS LINE                                                                       line.sub.-- c                                                                 EDGE anterior.sub.-- edge OF PLANE distal.sub.-- plane IS EDGE                posterior.sub.--                                                              edge OF PLANE anterior.sub.-- chamfer.sub.-- plane                            EDGE posterior.sub.-- edge OF PLANE distal.sub.-- plane IS LINE               line.sub.-- d                                                                 EDGE anterior.sub.-- edge OF PLANE posterior.sub.-- chamfer.sub.-- plane      IS EDGE                                                                       posterior.sub.-- edge OF PLANE distal plane                                   EDGE posterior.sub.-- edge OF PLANE posterior.sub.-- chamfer.sub.-- plane     IS LINE                                                                       line.sub.-- e                                                                 EDGE distal.sub.-- edge OF PLANE posterior.sub.-- plane IS EDGE               posterior.sub.--                                                              edge OF PLANE posterior chamfer plane                                         EDGE proximal.sub.-- edge OF PLANE posterior.sub.-- plane IS LINE             line.sub.-- f                                                                 #now define two free lines for the bore axes                                  POINT top OF LINE hole.sub.-- 1 IS .8,0,0.508                                 POINT bottom OF LINE hole.sub.-- 1 IS .8,0,2                                  POINT top OF LINE hole.sub.-- 2 IS -.8,0,0.508                                POINT bottom OF LINE hole.sub.-- 2 IS -.8,0,2                                 ______________________________________                                    

Each of these primitives is added to a list of template members. It ispreferable to check the data by checking each point of each of the linesof the planes for coplanarity with all other constituent points of theplane, as well as linking of all list members to be certain the file iscomplete. A variety of methods are known for performing such geometricintegrity checks. One method is to solve for the normal vector of theplane, determined by the first three constituent points encountered, andthen to check the dot product of the normal vector with the vectordefined by each subsequent point. If the product is nonzero, the pointis outside of the plane.

The tightness of the press fit can be modified, if desired, by modifyingthe information in the geometric database. For example, if it isdesirable to cut the femur end so that it is slightly larger than theprosthesis' inner surface, as is the current practice, the datacorresponding to the surface-cut relationships will be altered so thatthe cut positions are adjusted away from the proximal end of the femur.This data adjustment is entered in the database prior to the performanceof the procedure so that no adjustments need be made during the TKA.

Programs are written in VAL-II and stored in the supervisor orcontroller for use by the main surgical program. These contain thecommands for specific procedural steps such as positioning a tool in acut plane, moving the mounting flange to the nest, etc. The VAL-IIprograms can then be accessed by the main program during the procedure.The VAL-II programs, when accessed, are downloaded to the controller andexecuted.

In one preferred embodiment, the main surgical bone alteration programis written in a high level language as a task. A task program is of theform:

    ______________________________________                                        TASK task name                                                                action 1                                                                      action 2                                                                      .                                                                             .                                                                             ______________________________________                                    

Types of actions include:

DO a subtask

MAKE a named cut or hole

POSITION a template attached to the robot wrist

DEFINE a prosthesis' geometry database source

DEFINE a named cut or hole as a named feature of a template

One sample bone alteration surgical task that could control a bonealteration surgery is:

    ______________________________________                                        TASK leg            # perform the task on                                                         a leg                                                     DO select           # select a procedure                                      POSITION TEMPLATE leg                                                                             # position the template                                   DO cuts             # make the cuts                                           DO holes            # make the holes                                          ______________________________________                                    

The sample task could control a right knee TKA. Each of the actions mayreference one or more subtasks that will carry out the procedure. Forexample, in the "DO cuts" action, one of the subtasks would be to choosethe cut to be made; i.e., distal, proximal, etc. When the actionreferences a robot movement, the appropriate VAL-II programs aredownloaded to the controller and executed. The remainder of the controlsystem operation will be described after a discussion of the toolsutilized in bone alteration surgeries.

Once the bone is immobilized, the position of the femur must be taughtto the robot. A prosthesis template is used for this task. Withreference to FIG. 15, the template 200 includes an attachment flange201, a horizontal plate 202, two separated vertical plates 203 and 204,and a stabilizing plate 205. The plates are secured to one another bypins 206. In practice, the template is mounted to the coupler, and therobot mounting flange and the template are positioned adjacent theexposed femur end. A cut bone 12 is shown to illustrate the relationshipbetween the template inner plate edges and the surface cuts. Thisrelationship corresponds to the relationship between the prosthesisexterior and interior surfaces.

The template is constructed so that it generally fits over the existingfemur anatomy. This is of particular value in situations where largeamounts of the bone surface have been lost to disease or damage, sincethose situations greatly hinder visualization of the completed, implantwhen using the conventional jig systems.

The template includes cut-guide marks 207 and rod-alignment tabs 208 toenhance the alignment and visualization processes. The cut-guide markscorrespond to the anterior, distal and posterior planes that define theinner surface of the prosthesis. Thus, the surgeon can visualize whetherthere will be any problems with making adequate surface cuts in the boneto allow proper fitting of the prosthesis. For example, if a large notchis present in one condyle, the surgeon can mentally extend the distalcut-guide mark to determine whether, with a given cut plane, enoughhealthy bone is present to provide a loaded fit of the prosthesis.

The rod-alignment tabs 208 can be used to attach a straight rod abovethe center of the implied prosthesis position, and perpendicular to thedistal cut plane. The tabs are extensions including slots that runparallel to the distal-proximal axis. The slots are dimensioned so thata conventional alignment rod can be set between them. By adjusting thetemplate position, the rod can be aligned with the longitudinal axis ofthe femur.

With reference to FIG. 16, the inner edges 210-212 of the templatecreate an inverse image or mold of the prosthesis exterior surface.Three contoured edges are adequate to define the major contours of theprosthesis exterior surface. Thus, the inner edges of the templatecorrespond to the exterior portion of the prosthesis. Additional platescan be used to define the contours in greater detail provided the platesallow the surgeon to easily view the bone and the inner edges from avariety of angles.

The horizontal edge 210 has concave side edges corresponding to thecondyles and a flattened convex central edge corresponding to the notchmargin. The vertical edges 211 and 212 are concave and correspond to theanterior-to-posterior line of the condyles.

With reference to FIG. 17, the vertical edge 211 closely conforms to arelatively normal femur end. If the bone is damaged, e.g., a large notchexists in the condyle, the edge 211 allows the surgeon to visualize whatthe prosthesis surface will look like relative to the existing bone. Thecut-guide marks are extended in reference through the bone. Thecut-guide marks aid the surgeon in visualizing the prosthesis innersurface relative to the template position.

With reference to FIG. 18, the contours of the horizontal plate edge 210follow a medial-lateral contour line across the distal end of the femur.The positions of the lower portions of the vertical edges 211 and 212relative to the positions of the concave portions of the horizontal edgeprovide the surgeon with a variety of reference lines for visualizingthe continuous contours of the prosthesis outer surface.

The cut-guide marks and plate edges assist in positioning four degreesof freedom of the prosthesis: anterior-posterior, distal-proximal, andmedial-lateral translation; and axial rotation. The alignment rodassists in positioning the flexion-extension and varus-valgus rotations.The template is preferably made of transparent plastics, such asPLEXIGLAS, thermoplastic poly(methyl methacrylate), which allow thesurgeon to easily visualize the relationship between the femur and theprosthesis by viewing the inner edges of the template and the cut-guidemarks.

In operation, the template attachment flange 201 is attached to thecoupling block of the coupler and, thus, to the robot by means ofthumbscrew 209. The alignment bores (not shown), of the attachmentflange are inserted over the alignment studs of the coupling block. Thetemplate identification is checked by reading the identification pattern(not shown) on the attachment flange. In one method, the robot arm isthen freed from all mechanical locking of the joints, i.e., set to apassive mode, so that the surgeon can manually position the templaterelative to the femur. The encoders remain active throughout thepositioning step. The positioning is a subjective determination by thesurgeon aided by the template. The inner edges of the template arepositioned in the desired position of the exterior surface of theprosthesis. After the surgeon has positioned the template to his or hersatisfaction, the robot is set to the active mode wherein theservomotors are active, and wherein robot movement occurs in response tomovement commands received from the controller. The controller thenreads the position of the template in the world coordinate system. Thisreference position is stored in the supervisor memory. An alternativemethod of positioning the template is to control the movement of themanipulator by some remote means such as the teaching pendant or ajoystick so that the robot remains in an active mode throughout thetemplate positioning task.

The bone alteration program may provide an additional positioning aid.Once the template is positioned by the surgeon, either in the passive oractive mode, the surgeon may desire an extremely slight adjustment.Rather than physically moving the template, the program can accept areference position modification command. The modification, e.g., 1 mmtranslation along the Z-axis defined in the tool coordinate system, isapplied to the reference position, and a new reference position isgenerated which reflects the modified position. Such a positionmodification procedure is desirable when an x-ray of the positionedtemplate is made and analyzed. Modifications according to the x-ray maybe made more exactly through the program than by physicallyrepositioning the template.

An additional decision-making aid can be incorporated into the bonealteration program. An expert system, that uses a knowledge base relatedto the bone alteration surgery is incorporated into the bone alterationprogram. For example, a definite and quantitative relationship betweenthe amount of bone removed from the tibia and the varus/valgus flexityof the knee is determinable. By incorporating this and similarrelationships into the bone alteration program, the surgeon is advisedby the program of the biomedical consequences of the contemplatedsurgical operation to the bone. The expert system utilizes the referenceposition established by the procedure to determine the relevantinformation to be provided to the surgeon. Alternatively, the bonealteration program suggests modifications to the ongoing procedure whichwould improve the clinical outcome. If the surgeon approves of thesuggested modifications, the positioning of surgical tools is modifiedthrough the program. These and other bone alteration programmodifications and enhancements are made according to the requirements ofthe specific procedure and the availability of additional information,such as the data necessary to establish an expert system.

One robot safety feature that is available using the bone alterationprogram is the concept of a "safe sphere." This is an area of apreviously defined dimension that surrounds the learned position of thebone. The robot will only enter the sphere if it is commanded to do so,and will move within the sphere only along a straight line; i.e., towardthe line corresponding to the approach edge that is defined for each cutand bore defined in the geometric database. When retreating from thesafe sphere, the robot will retreat along the same line. Rotational andtranslational motion of the tool takes place only outside of the safesphere, thereby protecting the femur and exposed knee from damage causedby inadvertent touching or striking by the tool.

Once the template is positioned in the desired position, and thereference position recorded, the next step in the procedure is to makethe bone cuts and/or bores. The tools for the cutting and boring taskswill be immediately described, while the methods for determining theposition of and actually positioning the tools will be discussed in alater section.

As illustrated in FIG. 19, saw guide 215 is mounted on coupling block164 and positioned near the end of the femur. The saw guide includesattachment flange 217 and guide plates 219. In one preferred embodiment,the saw guide is connected by anchor pin 221 to stabilizing device 73. Asaw blade 222 is shown in a cutting position.

In one preferred embodiment, the saw guide is crescent shaped so that itcan be used near a bone end in a manner that minimally interferes withthe overall view of the bone. The crescent shape allows the guide to beplaced relatively close to the bone and allows the saw blade to approachthe bone from a range of angles. The surgeon can see the entry point ofthe blade. While the saw guide ts shown positioned and oriented for ananterior cut, the same guide is used to guide the saw blade in each ofthe cut planes.

A surgical saw blade fits between and is held in the plane of the guideplates so that the movement of the blade is limited to one planealthough the blade is allowed to move freely within the plane. Thus, ifdamaged bone, blood vessels, flesh, etc. lie in the cut plane, thesurgeon is free to manipulate the blade within the cut plane to avoidthose specific portions of the knee.

In a preferred embodiment, the system includes a stabilizing device 73to secure the end of the saw guide that is opposite the attachmentflange 217. With a small robot or a robot manipulator with slightlymovable joints, it is desirable to provide an additional support for themanipulator. The need for additional support arises from the complianceof the manipulator, limited strength of the servomotors, and/or backlashin the gear trains. The PUMA 200 robot, as an example, is essentially acantilevered beam extending from its base, so even relatively smallforces applied to the saw guide produce movements large enough toovercome the effective stiffness of the robot.

In one preferred embodiment that is additionally illustrated in FIG. 4,the stabilizing device 73 includes a bridge rod 224, two pin block 226and rod block 228 pairs. One pin block is attached to the immobilizer bystabilizing pin 101 secured into one of a series of bores through thelower frame of the immobilizer, the bores being perpendicular to theframe surface. Alternatively, the bridge rod is connected to theoperating table or other device that provides a stable reference point.The other pin block is attached to anchor pin 221. The pin and rod blockpairs are Joined by thumbscrews 230 that slide through the pin block andscrew into the rod block. The pin block can rotate about the thumbscrew.Each block has a bore and slit perpendicular to the thumbscrew. Thebridge rod slides through the red block bores. The blocks are tightenedabout the pins and rod by the tightening of thumbscrews 230. The pin androd block pairs, combined with the variety of positions along the frameinto which the stabilizing pins 101 can be secured, provide adequatedegrees of freedom so that the bridge rod can be connected to the sawguide and the frame regardless of the position of the saw guide.

The necessity of a stabilizer depends on the relative rigidity providedby the device to which the saw guide is mounted. It is beneficial to theaccuracy and efficiency of the saw guide to provide a stabilizer for thefree end. This benefit is balanced with the time that it takes to adjustand secure the stabilizer during the procedure.

In one preferred embodiment, the stabilizing bridge rod provides anadditional safety feature. The saw guide, immobilizer and stabilizer aremade of electrically conductive materials and form a simple ground loopdetection circuit when the stabilizer is attached to the saw guide andthe immobilizer. A portion of the wiring in cable 58a carries signalsindicative of the status of the circuit. The signals are received atcontroller input/output port 60. The controller can determine whetherthe saw guide, and, thus, the manipulator is rigidly connected to thestabilizer. The bone alteration program checks this circuit statusbefore allowing the saw guide to be moved once it has been positionedadjacent the patient. If a move command is received and the stabilizercircuit is complete, the program generates an error message thatindicates that the stabilizer must be detached before the move can beaccomplished. The stabilizer is alternatively attached to the operatingtable or some other structure that is rigidly positioned relative to thereference structure. When the stabilizer is connected to an electricallyconductive structure, the safety circuit can be utilized. Additionally,other methods for determining whether the tool is braced, such as an LEDdetection array or microswitches could be used.

FIGS. 20 through 22 Illustrate one preferred construction of the sawguide 215. As shown in FIG. 20, the saw guide includes top plate 234,and bottom plate 236, inner liners 238, connector screws 240, shims 241and 242 and thumbscrew 243. The attachment flange 217 extends from oneend of the top plate. The plates are connected so that the distancebetween the plates is nearly equal to the thickness of the saw bladechosen for the operation.

The top and bottom plates are made of a rigid material, preferablystainless steel or other material that is suitable for use in thesurgical environment. The liners 238 are preferably made of alow-friction material, such as TEFLON, tetrafluoroethylene fluorocarbonpolymers. In one embodiment, the liners are permanently bonded to theplates by epoxy. Alternatively, the liners are provided with a strip ofadhesive 244 to attach them to the plates. The latter guide liners arepreferably disposable to avoid the need to resterilize them as well asto avoid wearing of the liners which may result in residue from theliners falling into the exposed area. By using adhesive strips 244, theliners can be easily attached and removed from the plates.

The guide liners are shaped to conform closely to the curve and radialdimensions of the inner surfaces of the top and bottom plates. As shownin FIGS. 20 and 21, the length of the liners is slightly shorter thanthe top and bottom plates so that slight recesses 245 are left betweenthe plates at each end of the guide curve. The recesses are useful whenthe teeth of the blade are slightly offset from the plane of the bladeso that it is difficult to pass the teeth between the lined plates. Thetoothed edge of the blade is passed between one of the end recesses toposition the blade for cutting. The liners extend far enough to theguide ends so that the recesses are not large enough to allow the bladeto slip outside of the lined area. Alternatively, the ends of the guideplates remote =from the attachment flange are not connected together.The saw blade then slides through this opening. A suitably rigidmaterial must be used for the guide plates in this configuration.

A default blade thickness capacity ts dictated by the height of ledges246 and 247 on the top plate and the thickness of the liners. Thedistance between the plates can be increased to accommodate blades ofvarious thicknesses. One or more shim pairs 241 and 242 can be insertedbetween the top and bottom plates to increase the distance between theliners. The shims are secured between the guide plates by connectorscrews 240.

With reference to FIGS. 21 and 22, pin guides 248 extend through the topand bottom plates and are suitable for receiving pins 249. The pinguides lie in the plane of the guide plates. The pins provide analternative saw guide stabilizing means. The pins can be strategicallypositioned through the saw guide and tapped into the bone to secure theguide relative to the bone. The pins do not interfere with the cut planeor with the surgeon's view of the area.

As shown In FIG. 23, the saw blade fits snugly between liners 238. Theguide plates and attachment flange do not obstruct the view of thecutting edge of the blade which extends beyond the guide plates.

FIG. 24 illustrates a drill guide 252 used in the present system. Thedrill guide includes an attachment flange 254, a reference plate 256, athreaded bit guide 258, and pin guides 260. The reference plate isperpendicular to the axis of the bit guide 258. The attachment flange ofthe drill guide is similar to that of the saw guide, with theidentification pattern identifying it as a drill guide. The attachmentflange ts connected to the coupling block by a thumbscrew (not shown).Preferably the bores are made after the distal cut, but that is notrequired. The bit guide axis need only be aligned with the bore axis andthe guide positioned near the bone to successfully complete the drillingtask. Bit fitters of different diameters are available and can bescrewed Into the bit guide so that the drill guide can be used with avariety of bit sizes.

Once the drill guide is attached to the robot and the identificationchecked, the robot positions the guide for the specific bore, i.e.,medial, lateral, center, etc., according to the surgeon's choice. Therobot positions the drill guide so that the reference plate ts againstthe distal end of the bone. Once the drill guide is positioned, it isfurther stabilized by tapping pins 262 through pin guides 260.Alternatively, the unattached drill guide is positioned manually andsecured by pins or other stabilizing means.

Once the drill guide is in place, the bore is drilled. Often, the depthof the drill is gauged by a notch on the bit itself that corresponds tothe length of the bore plus the length of the bit guide. Obviously, themark must also take into account whether the guide is to be positionedbefore or after the distal cut is made. Each additional drilling task iscarried out in a similar manner.

The integration of the template, saw guide, and drill guide into arobot-aided bone alteration surgery will now be described.

Once the leg is situated through the immobilization device, the knee isopened and the femur immobilized. The robot is then taught the desiredtask position on the femur. In a TKA, the task position corresponds tothe desired prosthesis position. Referring now to the flow chart of FIG.25, the bone alteration program is initiated on the supervisor. At thosesteps in the program where the surgeon is provided with options, thechoice is indicated during surgery by the surgeon touching the TouchWindow screen at a point corresponding to the option.

The first step is to choose a task, which, in the instance of a TKA,requires choosing a prosthesis. This is done at the select componentstep. The corresponding prosthesis template is mounted on the coupler asdescribed above. The identification pattern on the template attachmentflange is checked against an identification code database in thesupervisor. The identification pattern is obtained by polling the signalfrom the identification component at the input/output port. If theidentification code is correct, the control system moves onto the nextstep. If the identification is incorrect, the control system will signalan error to the surgeon, and allow the surgeon to quit the program or toproceed once the proper template is attached.

Once the template is attached, the prosthesis task or position is taughtto the robot. In the preferred method, the robot is switched to apassive mode wherein the robot manipulator is manually manipulated. Inthe passive mode the servomotors in the robot Joints are unpowered andthe incremental encoders in the joints are still active. The passivemode is provided by the manufacturer to be used during the extraction ofa robot manipulator from a difficult crash situation. However, in thissystem, the robot ts placed in the passive mode and the surgeon isallowed to control the template position manually by manipulating therobot manipulator.

Since the immobilization device allows the knee to be established in avariety of positions, there is no method for preprogramming the robot tomove the template to the proper position relative to the femur end.However, alternative, nonmanual movement control methods, such as usingthe teach pendant or a joystick, could be used. The preferred method isadvantageous because it is relatively quick and allows the surgeon agreat deal of control over the precise position of the template withoutthe necessity of generating a number of movement commands through thecontroller.

Once the template is positioned, the joints are looked so that theposition can be considered by the surgeon. The unlocking and relockingstep is repeated until the position of the template is consideredsatisfactory. Once a satisfactory position is obtained and the positionlocked, the surgeon indicates that the template position should berecorded. The robot position sensors then transmit to the controller theposition of the template in the world coordinate system.

With reference to FIGS. 26 and 27, the next step is to cut or bore thebone. Once the cut task is chosen, the tool identification code is readto determine whether the saw guide has been attached. If the guide hasnot been mounted then an error is indicated to the surgeon. Once the sawguide is attached, the surgeon chooses the order of the cuts by choosinga cut type on the input screen. Once a cut is chosen, such as theanterior cut, the control system uses conventional geometrictransformations to integrate the anterior plane coordinates from thegeometric database with the reference position to determine the anteriorcut plane position in the world coordinate system. Then, working in areverse manner, the tool position in the world coordinate system for theanterior cut is determined by combining the cut plane position with thetool definition. The result is a position array corresponding to theproper position of the tool in the world coordinate system that willposition the saw guide for the anterior cut. The bone alteration programgenerates or provides variable values to a VAL-II program that isdownloaded to the controller. The controller processes the program andthe robot positions the saw guide accordingly.

As discussed above, once the saw guide is positioned, a stabilizingdevice is used to provide additional rigidity to the tool position.After the cut is made and the stabilizing device is disconnected, therobot is commanded to move to the next step.

The surgeon continues to command the robot to move the saw guide to theproper position for each of the cuts necessary for the bone preparation.Using this method, the surgeon is free to choose the order of the cuts.

With reference to FIG. 27, once the surgeon has indicated that boringwill be the next step, the bone alteration program will ascertainwhether the drill guide has been attached to the coupling block. If thetool has been properly attached, the surgeon will be allowed tocontinue. The surgeon decides which bore is to be drilled first, andindicates the choice through the input screen. The program thendetermines the position of the drill guide in a manner similar to thedetermination of the saw guide position described above. A VAL-IIprogram is generated, downloaded to the controller, and executed. Therobot will then move the drill guide to the appropriate positionadjacent the femur. Once the guide is flush against the distal cut, itis preferable to stabilize the guide with reference to the bone toprevent slight movements during the boring procedure. The bone is thendrilled out, the stabilizing device is disconnected, and the robot iscommanded to move to the next step. If more than one bore is to be madein the bone, each bore is made sequentially according to the orderchosen by the surgeon.

Once the bores are completed, the femur preparation task is done and therobot returns to its resting position. The area of the knee is thencleaned out and the prosthesis attached to the femur. The knee is thensewn up.

A number of safety features are available using the present invention.One programmable safety feature is to command the robot through the bonealteration program to position the tool a predetermined distance awayfrom the bone, such as 10 cm, rather than commanding the robot toinitially position the tool in what is calculated to be the desiredposition. For example, during a cutting procedure, the bone alterationprogram generates a tool position command that will place the toolrelatively near the femur. The program then adds a translationaldistance to one of the coordinates of the position so that the saw guideis initially oriented in the proper plane, but is positioned apredetermined distance away from the femur. The translation is along thesame coordinate axis along which the tool moves in the safe sphere. Thesurgeon then uses the input screen to move the tool closer to the bonein incremental steps until the surgeon is satisfied with the bone-toolrelationship. The initial position of the tool will be within the safesphere so that all movement closer to the bone will be in a plane and norotation of the tool will be done. Thus, the surgeon can position thetool at the most advantageous position for the specific cut.Additionally, using this method, the robot is not relied upon to makecontact type positioning such as placing the drill guide flush with thedistal cut.

The safety stand and stabilizer circuit allow for automated continuouspolling of the status of the robot. During robot movement, thecontroller continuously polls the signals on cable 58b connected to therobot safety stand. If the signals indicate that the stand has tiltedenough to break one of the circuits then the supervisor will shut offpower to the robot so that all movement ceases. Additionally, when amovement command is received during the bone cutting procedure, thecontroller polls the signals on Cable 58a connected to the mountingflange. If the signals indicate that the robot is attached to thestabilizer, the program will not allow a move command to be executed.This prevents the manipulator from moving when it is secured to anotherstructure.

The present Invention has been described in terms of a TKA procedure. Itis to be understood that the system of the present inventions can beapplied in many procedures. The one aspect of the system that must bemodified to match a specific procedure is the configuration of thetemplate. The template used in each specific procedure is used to teachthe robot the position and orientation of some aspect of the procedure.

For example, the system is applicable to osteotomy and ligament repairprocedures. In an osteotomy, a wedge of bone is removed from one side ofa bone so that the bone is shortened on that side. The cut areas arethen brought together so as to change the axis of the bone. The surgeonmust determine the area of the bone from which the wedge is to beremoved and additionally determine the dimensions of the wedge. Anelongated template having a side that represents the exterior surface ofthe bone is one suitable template. The template includes a center markthat is aligned by the surgeon with the center of the wedge. Thetemplate also includes a vertex pointer. Thus, features of the templateindicate the desired position of the center of the wedge surface and ofthe vertex. The geometric database for the osteotomy includes thegeometric relationships between the two cut planes that define thewedge. The position of the cut planes will be relative to some point andorientation of the template. As in the TKA procedure, the leg would beimmobilized and the area of the surgery exposed. Once the template ispositioned relative to the bone, the reference position is recorded. Thesurgeon then indicates to the program the angles of the wedge to be cut.Using the angle data and reference position, the robot can be commandedto position a saw guide for each cut of the wedge. The cuts arepositioned symmetrically about the point or line on the bone that wasindicated by the center mark on the template. The above-described bonealteration surgical task would be run. At the "DO select" action, anosteotomy would be chosen. The "DO holes" action would not be necessary.The task would execute the appropriate VAL-II program for an osteotomy.

In one type of ligament repair, a bore is drilled completely through abone or set of bones, and ligament material is stretched through thebone and secured. One template configuration useful for such a procedureis a pointer. The pointer tip represents the position of a bore endrelative to the bone. The pointer is used to indicate two referencepoints. The geometric database for ligament repair includes a line thatrelates to the template point feature in that the line extends betweenthe two reference points. Again, the leg is immobilized and the area forsurgery is exposed. The template is then positioned so that the tip ofthe template points to or rests on the bone area, first at one bore endand then at the other. Each position is recorded. The program thendetermines the proper position and orientation of the drill guidemounted to the robot mounting flange for carrying out the drilling taskso that the bore extends between the two bore entry points. Theabove-described bone alteration surgical task would again be run. Aligament repair procedure would be chosen, and only the "DO bores"action would be available. A VAL-II program is generated at the "DOcuts" action, the program is downloaded and executed to move the tool tothe proper position.

While preferred embodiments of the invention have been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.For example, a variety of robots, controllers and supervisors couldimplement the system. The system can be used for other bone alterationprocedures by using appropriate templates. Additionally, the toolidentification device could utilize Hall-effect switches, microswitches,or other methods for carrying out proximity detection.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A prosthesis templatefor aiding in the determination of a desired position of a prosthesisrelative to a bone and for additionally aiding in determining the properpositions of bone cuts necessary to prepare the bone to receive theprosthesis, the prosthesis having an exterior surface that simulates theexterior surface of the bone and an interior surface comprised of one ormore contact surfaces to which the prepared bone must conform to providean adequate fit of the prosthesis, said template comprising a templatemember having an interior surface, said interior surface correspondingto an exterior surface of the prosthesis, whereby said template can bepositioned adjacent the bone and thereby provide means for evaluating adesired position of the prosthesis exterior surface, said templatefurther including a cut-guide mark lying in a cut plane, therelationship between the cut plane and said interior surfacerepresenting the relationship between the prosthesis exterior surfaceand one contact surface of the prosthesis, whereby said template can bepositioned adjacent the bone and thereby provide a visual means forevaluating the proper position of the prosthesis interior and exteriorsurfaces.
 2. A template as claimed in claim 1, wherein said templateinterior surface is defined by three contour lines.
 3. A template asclaimed in claim 1, further comprising longitudinal alignment means forproviding a reference between said template and the longitudinal axis ofthe bone.
 4. A template as claimed in claim 1, wherein said templatemember is comprised of rigid transparent material.
 5. A template asclaimed in claim 1, further comprising mounting means for rigidlysecuring said template relative to a reference structure.